Thermodynamics
This Chapter is related to Thermal Physics For Chemistry Section , go to Chemical Thermodynamics Heat The energy that is transferred from one body to another , without any mechanical work involved , is called heat . Heat is meaningful as long as there is transfer of energy . Unit : Joule , Calorie 1 Calorie = 4.18 Joule Scales of Temperature Celsius Fahrenheit Kelvin Thermal Expansion (All temperatures in oC) Linear Expansion Areal Expansion Volume Expansion Calibration of Thermometers 1) Mercury Thermometer : ''' Mercury thermometer works on the principle of linear expansion . A certain change in temperature brings a certain change in length of mercury column . This change can be easily calculated by the formula of linear expansion , if we know the coefficient of linear expansion of mercury and its original length at 0o C . '''2) Electric Thermometer : The resistance of the thermometer coil changes with changes in the temperature . This change is detected by an external circuit , responsible for displaying the temperature . Calorimetry Calorimetry is the measurement of heat i.e. energy transferred between two bodies . The principle of Calorimetry states that the total heat energy given by the hot objects equals the total hat energy absorbed by cold body . Specific Heat Capacity c = Q / m∆θ cv = Q / m∆θ cp = Q / m∆θ cp - cv = R cm = Q / n∆θ Molar Specific Heat Capacity γ = cp/cv Latent Heat The heat energy required to change the state of matter is called as Latent hat of Fusion . Specific Latent Heat = Q / m Mechanical Equivalent of Heat W = J H where Work W produces same temperature change as Heat H and J is a constatn called as mechanical equivalent of Heat . Thermal Conductivity Thermal Conductivity Q = KA∆θ/xt , where K is the thermal conductivity . Thermal Resistance Q/t∆θ = KA/x above equation t∆θ / Q = x/ KA t∆θ / Q = R where R is the Thermal Resistance (Reciprocal of KA/x) Series Connection : R = R1 + R2 + R3 + .... + Rn Parallel Combination : 1/R = 1/R1 + 1/R2 + 1/Rn + .... + 1/Rn Convection and Radiation Convection is the process of transfer of heat by the actual mobility of particles . Radiation is the emission of electromagnetic waves of frequency υ and energy hυ or hc/λ . The speed of an radiation is equal to the speed of light . Newton's Law of Cooling Rate of Cooling = K (θ - θo) Newton's Law of Cooling is applicable only for temperature difference of less than 10o C Prevost Theory of Exchange # A body having temperature equal to it's surroundings , radiates energy at the same rate as it absorbs energy # A hot body placed in cool surroundings , radiates energy faster than what it absorbs . # A cool body placed in hot surroundings , absorbs energy faster than what it radiates . Zeroth Law of Thermodynamics Zeroth Law of Thermodynamics states that if two bodies P and Q are in thermodynamic equilibrium , and also P and R are in thermodynamic equilibrium then , Q and R are also in Thermodynamic Equilibrium . Isothermal & Adiabatic Processes Bulk Modulus of Gases Laws of Thermodynamics 1) ∆U = q + W 2) Mechanical Work can be converted completely into heat energy , but heat cannot be completely converted into mechanical work . i.e. heat and mechanical energy are not equivalent . 3) Th entropy of a perfectly ordered crystalline substance at absolute zero temperature is zero . First Law of Thermodynamics and it's Applications (For ideal gases only) Heat Engines An heat engine works in cyclic process . It takes heat from bodies at higher temperature , converts part of it into mechanical work and and remaining to a body at lower temperature . Efficiency of Heat Engine (η) = W / Q1 ; where Q1 is the heat input and Q2 is the heat output . W = Q1 - Q2 η = 1 - Q2 / Q1 T1/T2 = Q1/Q2 Refrigerators A refrigerator is the reverse of a heat engine . The refrigerator extracts heat (Q2) from cold reservoir at temperature T2 , external work W is done on it and Q1 is released to hot reservoir at temperature T2 . α = Q2 / W W = Q1 - Q2 α = Q2 / Q1 - Q2 Carnot Cycle Absorption and Reflection Q = Qa + Qr + Qt Coefficient of absorption (a) a = Qa / Q Coefficient of reflection ® r = Qr / Q Coefficient of transmission (t) t = Qt / Q 1 = a + r + t Athermanous Substances The substances which do not transmit any incident heat radiations are called as athermanous substances . Diathermanous Substances The substances which are transparent to heat radiations are called as diathermanous substances . Perfectly Black Body Perfectly black body is a body which completely absorbs all the radiant energy incident on it . Emissive Power and Absorptive Power Absorptive Power = a = Qa / Q Emissive Power = E = Q / At Emissivity = e = E(body) / E(PBB) Kirchoff's Law of Radiation E(body) / a = E(PBB) a = e Wien's Displacement Law λm = b/T b = 2.898 x 10-3 mK Steffan's Law of Radiation Q = σAT4 (for PBB) Q = σeAT4 σ = 5.67 x 10-8 Wm-2K-4Category:Physics